Roller mill control system

Abstract

A control system (44, 112) particularly adapted to be cooperatively associated with a mill (10) and in particular a roller mill (10) of the type that is operative to effectuate the grinding and/or pulverization of solid materials. When so employed, the subject control system (44, 112) enables the roller mill (10) to be operated over a wide range of varying levels of output of pulverized material, while yet ensuring that both the proper air/solids ratio and the desired degree of fineness of the pulverized material are being maintained. To achieve this result, the subject control system (44, 112) is operatively connected in circuit relation with the feed means (12) that supplies to the roller mill (10) the material that is to be pulverized therein, with the drive means (20, 22) through which the mill (10) is driven, with the classifier means (38) that effects a separation of the pulverized material according to fineness, and with the means which receives the output from the roller mill (10).

What is claimed is: 
     
       1. In the combination of a roller mill operative for grinding materail therewithin and feeder means operative for feeding to the roller mill the material to be ground therewithin, the roller mill including a mill motor for driving the roller mill and a classifier for classifying material ground in the roller mill, the improvement comprising a control system for effecting control over the rate of feed of material to the roller mill in accordance with the rate of output of ground material being demanded from the roller mill, said control system comprising: to the a. demand sensing means mounted in juxtaposed relation to the path of flow of ground material being discharged from the roller mill in the form of output therefrom, said demand sensing means including sensing means and a fuel indicating controller connected in circuit relation wilh said sensing means and having a manually set set point, said sensing means being operative to sense the output of ground material being demanded from the roller mill, said fuel indicating controller being operative to generate a signal representative of the output of ground material being demanded from the roller mill as sensed by said sensing means;   b. feed control means operative for controlling the rate of feed of material to the roller mill, said feed control means being connected in circuit relation with said demand sensing means for receiving said signal from said fuel indicating controller, said feed control means in response to said signal received thereby from said fuel indicating controller being operative to effectuate any changes in the rate of feed of material to the roller mill that may be required in order to conform the rate of feed of material to the roller mill to the rate of output of ground material being demanded from the roller mill as changes occur in the rate of output of ground material being demanded from the roller mill;   c. airflow measuring means operative to measure the airflow through the roller mill, said airflow measuring means including interconnected in circuit relation one with another a roller mill airflow sensor and a pressure transmitter and an airflow indicating controller having a self-corrected set point and a control linkage and a fan damper and linearization means, said airflow measuring means being connected in circuit relation with said demand sensing means for receiving said signal from said fuel indicating controller, said airflow measuring means in response to said signal received thereby from said fuel indicating controller being operative through the manipulation of said control linkage and said fan damper to effectuate as established by said airflow indicating controller any changes in the amount of airflow through the roller mill that may be required in order to maintain the desired air-to-solids ratio in the roller mill as changes occur in the rate of output of ground material being demanded from the roller mill that result in changes being made by said feed control means in the rate of feed of material to the roller mill;   d. pressure measuring means operative to measure the differential pressure across the roller mill, said pressure measuring means including interconnected in circuit relation one with another a roller mill pressure sensor and a pressure transmitter and a pressure indicating controller having a self-correcting set point and linearization means, said pressure measuring means being connected in circuit relation with said demand sensing means for receiving said signal from said fuel indicating controller, said pressure measuring means in response to said signal received thereby from said fuel indicating controller being operative to effectuate as established by said pressure indicating controller any changes in the value of the differential pressure across the roller mill that may be required in order to maintain the desired differential pressure across the roller mill as changes occur in the rate of output of ground material being demanded frmom the roller mill;   e. mill motor control means operative for controlling the speed of the mill motor;   f. classifier control means operative for controlling the mode of operation of the classifier; and   g. feed forward circuit means including differentiation means and summation means, said feed forward circuit means being connected in circuit relation with said mill motor control means and said classifier control means such that said summation means is connected in circuit relation with both said mill motor control means and said classifier control means and said differentiation means is connected in circuit relation with said summation means and therethrough to said mill motor control means and said classifier control means, said feed forward circuit means further being connected in circuit relation with said demand sensing means for receiving said signal from said fuel indicating controller, said feed forward circuit means being operative when said signal evidences the occurrence of a rapid change in demand per unit time of the output of ground material beind demanded from the roller mill to effectuate as established by said differentiation means and said summation means an anticipation and modulation of the speed of the mill motor as well as the operation of the classifier to prevent the roller mill from being subjected to a condition wherein there occurs either an overfeeding of the roller mill or an underfeeding of the roller mill relative to the rate of feed of material to the roller mill that is required in order to conform the rate of feed of material to the roller mill to the rate of output of ground material being demanded from the roller mill.   
     
     
       2. In the combination as set forth in claim 1 wherein said feed control means includes a feed transmitter and a feed indicating controller having a manually set set point, said feed control means being connected in circuit relation with a gravimetric feed system that includes a weigh belt, a feeder motor and a feeder motor speed control means such that said feed transmitter of said feed control means is connected in circuit relation with said weigh belt and said feed indicating controller is connected in circuit relation with said feed transmitter and therethrough to said weigh belt and with said feeder motor speed control means and therethrough to said feeder motor. 
     
     
       3. In the combination as set forth in claim 1 wherein said feed control means is connected in circuit relation with a volumetric feed system that includes a feeder motor and a feeder motor speed control means. 
     
     
       4. In the combination as set forth in claim 1 wherein said mill motor control means includes a mill motor speed control means connected in circuit relation with the mill motor. 
     
     
       5. In the combination as set forth in claim 1 wherein said classifier control means includes linearization means and classifier motor speed control means, said classifier control means being connected in circuit relation with the classifier such that said classifier motor speed control means is connected in circuit relation with the classifier and said linearization means is connected in circuit relation with said classifier motor speed control means and therethrough to the classifier. 
     
     
       6. In the combination as set forth in claim 1 wherein said control system further includes means for selectively introducing new constants into said control system.